The ankle is a complex system of joints and multiple bones that supports the body’s weight and facilitates movement. It serves as the primary link between the lower leg and the foot. While the ankle region contains several articulations, only a few bones form the main hinge that allows the foot to move up and down. Understanding these bones clarifies the difference between the ankle joint and adjacent connections to the rest of the foot.
The Bony Structure of the Ankle Joint
The primary articulation, the talocrural joint, is formed by three bones: the tibia, the fibula, and the talus. The tibia (shin bone) and the fibula are the two bones of the lower leg. The tibia is the larger bone, bearing most of the weight, while the fibula is the smaller bone situated on the outer side. The talus is the uppermost bone of the foot.
The ends of the tibia and fibula create a bracket-shaped socket, called a mortise, which receives the talus. The bony protrusions on either side are the medial malleolus (from the tibia) and the lateral malleolus (from the fibula). These malleoli cradle the talus tightly, creating a deep connection.
The talus fits snugly into this socket, connecting the leg and the foot. Since the talus is wider at the front than at the back, this fit contributes to stability, particularly when the foot is pulled upward. This arrangement of the three bones defines the ankle joint.
The Tarsals and Foot Connection
The talus connects to a series of bones beneath it called the tarsals, which make up the rear and mid-foot. The largest tarsal is the calcaneus (heel bone), which sits directly beneath the talus. The articulation between the talus and the calcaneus forms the subtalar joint.
This subtalar joint is separate from the main ankle joint and allows the foot to adapt to uneven ground. The talus also articulates with the navicular bone anteriorly. The seven tarsal bones include the calcaneus, navicular, cuboid, and the three cuneiform bones.
The hindfoot, composed of the talus and the calcaneus, is the section closest to the ankle. The talus transmits the body’s weight from the lower leg down to the rest of the foot, allowing for flexibility and shock absorption during movement.
Ankle Movement and Stability
The ankle joint functions largely as a hinge joint, allowing for two main movements: dorsiflexion (pulling the foot upward) and plantarflexion (pointing the foot downward). The tibiotalar joint is the primary site for this motion.
The deep socket created by the malleoli provides inherent stability. During dorsiflexion, the wider anterior part of the talus is wedged into the mortise, making the ankle most stable. Conversely, the joint is less stable in plantarflexion because the narrower posterior part of the talus is held in the socket.
Rotation of the foot (inversion and eversion) occurs primarily at the subtalar joint. This joint allows for the complex rotational adjustments necessary for walking on diverse surfaces. The combined action of the talocrural and subtalar joints provides the full range of motion and stability required for human locomotion.